The reinforcing part or reinforcement of tires, especially tires for civil engineering machine, at the present time usually takes the form of a stack of one or more layers conventionally denoted “carcass layers”, “crown layers”, etc. These names for the reinforcing parts stem from the manufacturing process, which involves building a series of semi-finished products in the form of layers containing often longitudinal reinforcing threads which are then assembled or stacked to create an unfinished tire. The layers are produced flat, in large dimensions, and are then cut to suit the dimensions of a given product. The layers are also initially assembled in an essentially flat form. This unfinished tire is then shaped to give it the typical toroidal shape of a tire. Semi-finished products known as finishing products are then applied to the unfinished tire to obtain a product ready for curing.
This type of “conventional” method involves using, especially for the stage of building the unfinished tire, an anchor element (generally a bead core) to anchor or immobilize the carcass reinforcement in the bead area of the tire. For this type of method, therefore, a portion of all the layers forming the carcass reinforcement (or only some) are turned up around a bead core laid in the bead of the tire. This anchors the carcass reinforcement in the bead.
The widespread adoption by the industry of this conventional type of method, despite numerous variants in the way in which the layers are constructed and assembled, has resulted in those skilled in the art using a vocabulary based on this method. Hence the generally accepted terminology, typically including the terms “layers”, “carcass”, “bead core”, and “shaping” to refer to the transition from a flat profile to a toroidal profile, etc.
There are now in existence tires that do not strictly speaking have “layers” or “bead cores” by the definitions given above. For example, document EP 0 582 196 discloses tires constructed without the aid of semi-finished products in the form of layers. For example, the reinforcing elements of the different reinforcing structures are applied directly to the adjacent layers of rubber compounds, and the whole is then applied by successive layers to a toroidal core whose shape produces directly a profile close to the final profile of the tire during manufacture. There are therefore no “semi-finished” products or “layers” or “bead cores” in that type of tire. The basic products such as rubber compounds and the reinforcing elements in the form of threads or filaments are applied directly to the core. Since this core is torus-shaped, there is no need to form the unfinished tire to turn it from a flat profile to a torus-shaped profile.
Additionally, the tires described in that document have no “traditional” turn up of the carcass layer around a bead core. This type of anchoring is replaced by an arrangement in which circumferential threads are laid adjacent to said sidewall reinforcing structure, the whole being embedded in an anchoring or bonding rubber compound.
There are also methods which assemble on the toroidal core using semi-finished products specially adapted for rapid, efficient and simple laying on a central core. Lastly, it is also possible to use a mixture combining certain semi-finished products to create certain architectural aspects (such as layers, bead cores, etc.), while others are made by the direct application of compounds and/or reinforcing elements.
In the present document, in order to keep up with recent technological changes in both the manufacture and design of products, conventional terms such as “plies” (that is, layers), “bead cores”, etc., are advantageously replaced by neutral terms or terms independent of the type of method used. Hence the term “carcass-type reinforcement” or “sidewall reinforcement” is a good designation for the reinforcing elements of a carcass layer in the conventional method, and the corresponding reinforcing elements, usually applied to the sidewalls, of a tire built in accordance with a method that uses no semi-finished products. The term “anchor region” can refer equally well to the “traditional” turn-up of a carcass layer around a bead core in a conventional method, or to the assembly formed by the circumferential reinforcing elements, the rubber compound, and the adjacent sidewall reinforcing portions of a bottom region formed by a method using application on a toroidal core.
Regarding the usual design of tires for civil engineering type vehicle, the radial carcass reinforcement anchored in each bead is composed of at least one layer of metal reinforcing elements, these elements being approximately parallel to each other in the layer. The carcass reinforcement is usually capped by a crown reinforcement consisting of at least two working crown layers of metal reinforcing elements which, however, each form an intersecting angle with the next layer and form with the circumferential direction angles of between 10° and 65°. Between the carcass reinforcement and the working crown layers, there are usually two layers of reinforcing elements, those of one layer forming an intersecting angle with those of the next and having angles of less than 12°; the width of these layers of reinforcing elements is usually less than the widths of the working layers. Radially outward of the working layers are protective layers whose reinforcing elements are at angles of between 10° and 65°. The crown reinforcement itself is capped by a tread.
The term “axial” denotes a direction parallel to the axis of rotation of the tire, while “radial” means a direction that intersects the axis of rotation of the tire at right angles. The axis of rotation of the tire is the axis about which the tire rotates in normal use.
A circumferential plane or circumferential cutting plane is a plane perpendicular to the tire's axis of rotation. The equatorial plane or circumferential mid-plane is the circumferential plane passing through the centre or crown of the tread which divides the tire into two halves.
A radial plane is a plane containing the tire's axis of rotation.
The longitudinal direction of the tire, or circumferential direction, is the direction corresponding to the periphery of the tire and is defined by the direction in which the tire rolls.
Tires for civil engineering machines, as described above, are usually inflated to a pressure of between 4 and 10 bar for normal loads and dimensions.
In a radial tire, and more especially a very large tire, the carcass is subjected to large radial deformations causing large deflections, due particularly to the load carried by the tire.
The dimensions of such tires linked with the loads they carry when rolling under load thus give rise to tire deflections of around 40%. They can for example experience increases of load greater than 50% under dynamic load increases associated for example with braking in the case of loader type vehicles.
The deflection of a tire is defined by the radial deformation of the tire, or variation of the radial height, as the tire adjusts from an unloaded state to a statically loaded state, under nominal load and pressure conditions.
Deflection is expressed in the form of relative deflection, defined as the ratio of this variation of the radial height of the tire to one half of the difference between the outside diameter of the tire and the maximum diameter of the wheel rim measured at the hook. The outside diameter of the tire is measured under static conditions in an unloaded state at nominal pressure.
Loaders which are used in mines for filling dumper type vehicles are used in a particular way that involves limited rolling but with operations combining forward or reverse rolling with heavy braking because the bucket of the loader may be rising at the same time as the loader is braking.
The wish for ever greater productivity leads to displacements with severe accelerations and heavy braking, and therefore increasing stresses on the tires.
Vehicle oscillations occur during the various braking phases. Besides being uncomfortable for the driver, these can also reduce productivity if the driver has to wait for the vehicle to stabilize before proceeding to the next stage of his journey. This particularly tends to occur when the loader brakes before emptying its bucket into the dumper to ensure that the bucket arms do not hit the edge of the skip and damage the loader.